A highlight of Cook's email: he says Apple has joined the nonprofit Fair Labor Association, and is the first tech company to do so.

Here's the full note:

Team,

We've just released our sixth annual update on conditions in Apple's supply chain, and I want to personally share some of the results with you.

We insist that our manufacturing partners follow Apple's strict code of conduct, and to make sure they do, the Supplier Responsibility team led more than 200 audits at facilities throughout our supply chain last year. These audits make sure that working conditions are safe and just, and if a manufacturer won't live up to our standards, we stop working with them.

Thanks to our supplier responsibility program, we've seen dramatic improvements in hiring practices by our suppliers. To prevent the use of underage labor, our team interviews workers, checks employment records and audits the age verification systems our suppliers use. These efforts have been very successful and, as a result, cases of underage labor were down sharply from last year. We found no underage workers at our final assembly suppliers, and we will not rest until the number is zero everywhere.

We've also used our influence to substantially improve living conditions for the people who make our products. Apple set a new standard for suppliers who offer employee housing, to ensure that dormitories are comfortable and safe. To meet our requirements, many suppliers have renovated their dorms or built new ones altogether.

Finding and correcting problems is not enough. Our team has built an ambitious training program to educate workers about Apple's code of conduct, workers' rights, and occupational health and safety. More than one million people know about these rights because they went to work for an Apple supplier. Additionally, Apple offers continuing education programs free of charge at many manufacturing sites in China. More than 60,000 workers have enrolled in classes to learn business, entrepreneurial skills or English.

Finally, we are taking a big step today toward greater transparency and independent oversight of our supply chain by joining the Fair Labor Association. The FLA is a leading nonprofit organization dedicated to improving conditions for workers around the world, and we are the first technology company they've approved for membership. The FLA's auditing team will have direct access to our supply chain and they will report their findings independently on their website.

No one in our industry is driving improvements for workers the way Apple is today. I encourage you to take some time to read more about these efforts, so that you can be as proud of Apple's contributions in this area as I am. The details are online now at apple.com/supplierresponsibility.